Seminar: Efficient Power Control and Transmitter Linear Precoding in Wireless Networks

Thursday, November 5, 2009 - 11:00am - 12:00pm EST

Speaker: Dr. Chris Ng

Faculty Host: Professor Elza Erkip

Abstract

Interference management is a fundamental challenge in wireless communications. In this talk, we consider several power control and linear precoding schemes in wireless networks where the transmitters interfere with one another.

First, we consider a downlink cooperative MIMO cellular network, and investigate the maximization of a concave function of the user rates. A new linear precoding technique called soft interference nulling (SIN) is proposed, which performs at least as well as zero-forcing (ZF) beamforming. Unlike ZF, SIN allows the possibility of but overpenalizes interference. All base stations share channel state information, but each user's message is only routed to those that participate in the user's coordination cluster. SIN precoding is particularly useful when clusters of limited sizes overlap in the network, in which case traditional techniques such as dirty paper coding or ZF do not apply. The SIN precoder is computed by solving a convex optimization problem. A cellular line network model is considered, and SIN under partial network coordination can outperform full network coordination ZF at moderate SNRs.

In the second part of the talk, we consider a wireless ad hoc network where we study the minimization of packet completion times. A convex cost function of the completion times of the user packets are minimized by optimally allocating the users' transmission power subject to their respective power constraints. When channel knowledge is imperfect, robust power control is considered based on the channel fading distribution subject to outage probability constraints. The problem is shown to be convex when the fading distribution is log-concave in exponentiated channel power gains; e.g., when each user is under independent Rayleigh, Nakagami, or log-normal fading.

About the Speaker

Chris Ng received his B.A.Sc. in Engineering Science from the University of Toronto. He received his M.S. and Ph.D. in Electrical Engineering from Stanford University. Since 2009, he has been a Member of Technical Staff at Bell Laboratories, Alcatel-Lucent, in Holmdel, New Jersey. From 2007 to 2008, he was a postdoctoral researcher in the Department of Electrical Engineering and Computer Science at the Massachusetts Institute of Technology. He was a recipient of the 2007 IEEE International Symposium on Information Theory Best Student Paper Award, and a recipient of a Croucher Foundation Fellowship in 2007. His research interests include cooperative communications, joint source-channel coding, cross-layer wireless network design, optimization, and network information theory.